Sickle Cell Anemia

Dr. Kim Mulvihill

Published 4:00 am, Tuesday, May 11, 1999

1999-05-11 04:00:00 PDT San Francisco -- Sickle cell anemia is an autosomal recessive blood disorder. It's caused by sickle shaped blood cells which can clump together and stick in blood vessels, blocking the normal flow of blood. When blood vessels are clogged by these cells it causes intense pain in bones, muscles or the abdomen, known as a painful crisis.

Up to 8% of African-Americans carry the trait for sickle cell. Others at risk include anyone whose ancestors are from South and Central America, Cuba, Saudi Arabia, Turkey, Greece, India and Italy. A simple blood test is all that's needed to check for the trait.

Autosomal recessive conditions are only a problem when both genes at the site are affected by the mutation. A carrier is someone who has one normal gene and one mutated gene at the site. Carriers are usually normal because the normal gene is expressed over the mutated gene. When both parents are carriers of an autosomal recessive condition, they run a 25% chance of having an affected child, and a 50% chance of having a child who carries the trait.

The couple went through in-vitro fertilization (IVF) at the Weill Medical College of Cornell University in New York. A number of the woman's eggs were fertilized by the husband's sperm. After three days, one or two cells were removed from each embryo and the DNA was tested to see if the genes contained the mutation which causes sickle cell anemia. Only healthy embryos (unaffected or carriers) were then transferred to the woman's uterus. The couple had twin daughters born at term, healthy and free of sickle cell trait or disease.

By identifying and transferring healthy embryos, pre-implantation genetic testing helps parents avoid the difficult decision of whether to abort a fetus that is affected by a crippling disease. This technique has been used for nearly a decade, to test for other genetic conditions such as cystic fibrosis and Tay-Sachs disease.

Pre-implantation genetic diagnosis is expensive and technically difficult, yet offers tremendous hope for carrier couples who wish to have a healthy child. It will have even broader application as we discern the genetic basis of other diseases.